Add support for C# 6 keywords

[jamesqo]

C# 6 introduces 2 new keywords, nameof and when. I've updated the csharp.json file to include these keywords among the other ones that are currently recognized, such as typeof and sizeof.

[DustinCampbell]

Hi! Sorry for not replying sooner.

First, thanks very much for taking the time to submit a PR. Because this is a Microsoft-owned project, we're working on setting up the machinery to handle CLAs. Once that happens, would you be willing to sign one (if you haven't already)?

[jamesqo]

@DustinCampbell Sure! In fact I believe I've already signed the CLA (see here), so that shouldn't be a problem.

[DustinCampbell]

Great! Hopefully the CLA automation will simply recognize you as having already signed.

[dnfclas]

Hi @jamesqo, I'm your friendly neighborhood .NET Foundation Pull Request Bot (You can call me DNFBOT). Thanks for your contribution!
You've already signed the contribution license agreement. Thanks!

The agreement was validated by .NET Foundation and real humans are currently evaluating your PR.

TTYL, DNFBOT;

[DustinCampbell]

@jamesqo, we're on lockdown in master, so I'm going to rebase against dev. Thanks again for your contribution!

[DustinCampbell]

OK, I've rebased and submitted #192. Thanks for your contribution @jamesqo!